Bistable writing type storage tube wherein metal sections are disposed in the respective wires of the target mesh



1967 YOSHKAKI NAKAYAMA ETAL 3,358,171

BISTABLE WRITING TYPE STORAGE TUBE WHEREIN METAL SECTIONS ARE DISPOSED IN THE RESPECTI E WIRES OF THE TARGET MESH Filed Dec. 27, 1965 FIG.\ FKSBQ FlG.3b

United States Patent O 3,358,171 BISTABLE WRITING TYPE STORAGE TUBE WHEREIN METAL SECTIONS ARE DISPOSED ILlZIEgHE RESPEC I'IVE WIRES OF THE TARGET Yoshiaki Nakayama and Tatsuya Yamada, Tokyo, and TorakiclliKobayashi, Kawasaki-sin, Japan, assignors to Tokyo Shibaura Electric Co., Ltd., Kawasaki-ski, Japan, a corporation of Japan Filed Dec. 27, 1963, Ser. No. 333,886 Claims priority, application Japan, Dec. 28, 1962, 37/553,080 5 Claims. (Cl. 313-68) ABSTRACT OF THE DISCLOSURE A storage target disposed between the fluorescent screen and electron guns of a storage tube, the target being a flat mesh of Wires with apertures therebetween. A secondary-electron-emission material covers the lengths except on portions of one side of the mesh which contain metal sections which act to collect the secondary electrons emitted by said material as a ,result of bombardment.

This invention relates to a bistable writing type storage tube, that is, the storage tube which employs bistable writing with the aid of a maintaining beam, having an improved target.

In a prior bistable writing type storage tube a target was used comprising a back electrode consisting of a nickel mesh of about 100 wires/cm, for example, a coating of talc powder and the like having a thickness of about several tens microns and applied to one side of the back electrode so as to serve as a dielectric material forming a storage layer and a collector of the secondary electrons applied on the storage layer and consisting of an aluminum mesh of about 40 wires/cm, for example. Such a target was placed between electron guns which are a writing gun and a flood gun, and a fluorescent screen to form a bistable writing type storage tube, for example.

When the writing beam, which is produced by modulating the amount of the current or the degree of deflection of an electron beam emitted from an electron gun according to an input signal is caused to impinge with a high velocity upon a collector side of the target, the exposed surface or the storage surface of the dielectric material facing to the writing gun will emit'much more secondary electrons than the incident electrons and the emitted secondary electrons will be collected by the collector. In this case the storage surface will be charged positively to elevate the potential of the storage surface, thus creating a potential 'pattern dependent upon the amount of modulation. If a low velocity flood beam is caused to impinge upon the storage surface formed with the potential pattern, the potential of portions of the surfaceat potentials higher than the critical potential of the secondary-electron emission characteristic will be further increased until a condition of equilibrium is reached at about the collector potential since the ratio of secondary electron emission of said portions is larger than unity. Whereas the potential of portions at potentials lower than the critical potential will be decreased until a condition of equilibrium is reached near the cathode potential of the flood gun since the ratio of secondary emission thereof is smaller than unity. Thus the storage surface will be divided into and held at two high and low stable potential portions due to the bombardment of the flood beam. The high'potential portions transmit more flood beam to the fluorescent screen whereas low potential portions less flood beam thereby producing bright and dark or two tone patterns on the fluorescent screen.

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Inasmuch as these patterns correspond to the potential patterns maintained at high and low potentials, respectively, on the storage surface, they will not disappear so long as the impingement of the flood beam is continued.

Owing to complex construction, the prior art target having a back electrode requires very complicated manufacturing steps. In order to hold two stable potentials on the storage surface and further to provide visible images of high contrast on the fluorescent screen, it is preferable, during operating process, to maintain the collector at a potential of at least v. or higher with respect to the flood gun cathode and to maintain the back electrode at a potential nearly equal to that of the cathode. As a result there is a tendency of electric breakdown between said electrodes, between the portions of the storage surface maintained at substantially the same potential as that of the cathode and the collector, and between the portions of the storage surface maintained at substantially the same potential as that of the collector and the back electrode. Once such an electric breakdown occurs the aluminum mesh of that portion will be damaged eternally to lose eternally the function of that portion of the target.

In addition, higher resolution cannot be expected because it is dependent upon the number of wires of the collector mesh. Further, higher maximum writing speed cannot be also expected because it is dependent upon the electrostatic capacity between the storage surface and the collector, and between the storage surface and the back electrode. These factors have greatly limited the ability as well as the characteristic of the storage tube.

Accordingly it is one of the objects of this invention to eliminate the above described defects encountered in the prior art target and in the prior bistable writing type storage tube.

A further object of this invention is to provide a novel bistable writing type storage tube which is simple in construction and easy to manufacture.

A still further object of this invention is to provide a novel target, which when incorporated into the bistable Writing type storage tube of this invention, will be free from any damage of the collector.

Another object of this invention is to provide an improved bistable writing type storage tube having excellent resolution power and high maximum writing speed.

In accordance with this invention the above and further objects are attained by providing a target comprising a unitary structure of a dielectric material and a metallic mesh, said metallic mesh serving as the collector electrode.

The features of the invention which are believed to be novel are set forth with particularity in the appended claims. The invention itself, however, as to its organization together with further objects and advantages thereof may best be understood with reference to the following description taken in connection with the accompanying drawings, in which:

FIG. 1 illustrates diagrammatically the section of a target constructed in accordance with this invention and adapted to be utilized in a bistable writing type storage tube of this invention;

FIG. 2 shows diagrammatically the longitudinal section of a bistable writing type storage tube embodying this invention and utilizing the target shown in FIG. 1; and

FIGS. 30, b and 4a, b show other embodiments of the target for use in the storage tube of this invention.

Referring now to the accompanying drawings, there is shown in FIG. 1 an embodiment of the target for use in the bistable writing type storage tube of this invention. The target 1 comprises a metal mesh 2 consisting of 100 wires per centimeter, for example. Except for one part, the sides of each wire are covered by a coating of dielectric material 3 having a thickness of about several tens s), microns. It will be noted that the dielectric material 3 is coated in such a manner that it protrudes into the interstices or perforations between wires of the metal mesh 2 but does not clog them and that these protruded portions 4 act as the storage area to emit electrons when subjected to electron bombardment. Whereas the exposed side of the wire will act as the collector for the secondary electrons to collect the secondary electrons emitted from said dielectric material.

Inasmuch as such a target can be easily fabricated by any suitable well known method it is believed that detailed description about such method is unnecessary. For example, a nickel mesh having 100 wires per centimeter can be easily prepared by an electroforming technique, and in order to apply the dielectric material to the wires of the nickel mesh such that it will protrude into interstices without clogging them, any suitable dielectric material such as talc, zinc orthosilicate and the like may be applied by spray or precipitation technique. In prior targets it was required to use an aluminium adhering mesh, which had been prepared by a suitable method, e.g., upon the coating of the dielectric material applied on the wires of the nickel mesh, but according to the method of manufacturing the target of this invention it is only necessary to apply the dielectric material on the metallic mesh, thus simplifying its process of manufacturing.

The reason why the target, which is not even provided with the conventional back electrode as shown in FIG. 1, can be utilized in the bistable writing type storage tube and how the above described objects can be attained by its novel function will be considered hereunder by referring to a particular embodiment.

FIG. 2 shows diagrammatically an example of a bistable writing type direct viewing storage tube utilizing a target of the form shown in FIG. 1. As shown in FIG. 2, within a neck portion 11 at one end of an evacuated vessel are contained an electron gun 12 for emitting a writing electron beam, a deflecting system 13 for said beam and another electron gun for emitting a flood beam. At the other end of said vessel 10 are provided a fluorescent screen 15 and a target 1 embodying this invention, which is mounted close to one side of the fluorescent screen facing the electron guns.

Also a cathode 17 of the flood electron gun 14 is disposed in the neck portion and is maintained at a reference potential which is usually the earth potential (assumed to be zero potential). The intensity of the flood beam is controlled by impressing a negative potential with regard to the cathode 17 to a control grid 18 from a source of variable voltage 19. The cathode 20 of the electron gun 12 for emitting the writing beam is maintained at a negative potential of about 3000 volts, for example, Whereas the control grid 21 is maintained at a negative potential with respect to the cathode 20, which is supplied thereto from a source of variable voltage 22 through a resistor 23. The intensity of the writing beam can be controlled by varying said source of variable voltage 22, or by applying a signal voltage to the control grid 21 through a capacitor 24 or by the combination of these two means.

Each of the electrodes 25 and 26 is constituted by an electric conductive film coated on the inner surface of the vessel 10 and is respectively maintained at a potential Within a range from 150 volts to about 200 volts so as to cause the flood beam to uniformly impinge upon the entire surface of the target 1. An electrode 27 comprising a metal mesh is disposed between the electrode 26 and the target 1 and is impressed with a potential of about 250 volts so as to act not only as an ion repeller but also as an electrostatic shield between the electron guns and the target.

As mentioned above the storage surface 4 of the dielectric material 3 of the target 1, which is exposed to the electron guns, will emit secondary electrons when subjected to electron bombardment, and the metal mesh 2 is given with a variable potential of the magnitude up to about volts so as to act as the collector for said secondary electrons.

The fluorescent screen 15 comprises a transparent electric conductive film deposited on the inner surface of one end wallv of the vessel 10 and a fluorescent material applied on said conductive film, and is maintained at a potential of about several thousands volts by impressing a potential to the transparent electric conductive film.

The operation of the storage tube shown in FIG. 2 is asfollows:

The operation roughly comprises, writing, reading out and erasing operations but first it is assumed that the potential of the storage surface is maintained atzero volt as the result of the erasing operation.

In order to effect writing, the writing beam emitted from the writing gun 12 is deflected by the action of the deflecting system 13 to scan the target 1 whereby to form thereon a pattern of electric charge in the same manner as in an oscilloscope wherein a figure of bright line is formed on its fluorescent screen. More particularly, when the writing beam impinges upon the storage surface 4, the surface will emit the secondary electrons which are collected by the exposed portion of the metal mesh, or the collector 2. But since the cathode 20 of the electron gun for emitting the writing beam is maintained at a potential of about 3000 volts, the ratio of secondary electron emission is higher than unity so that the potential of the portions of the storage surface which has been bombarded by the writing beam will build up from zero volt in the positive direction. This rate of potential build up is determined by such factors as the intensity of the writing beam, speed of deflection, an electrostatic capacity between the portion of the storage surface of said target, which has been bombarded by the writing beam, and the collector, the ratio of the secondary electron emission of the storage surface and the like. Reading out operation after writing operation is effected by the action of the flood beam emitted from the flood gun 14. As the cathode 17 of the flood gun is maintained at zero volt, the potential of the electrons at the moment of bombardment of the storage surface is equal to the potential of the storage surface. If the potential of the portion of the storage surface which has been subjected to the writing operation is at a suf ficiently high potential, the surface would be at a potential above the critical potential of the secondary elec tron emitting characteristic resulting in a secondary electron emission ratio larger than unity. As a result the potential of thisportion will further be increased by the action of the flood beam until finally a condition of equilibrium near the potential of the collector is reached. Whereas the otential of the portions not bombarded by the writing beam will remain at substantially zero volt so that the ratio of secondary electron emission thereof will be lower than unity thus continuing to maintain the potential of. said portions at about zero volt. In this way the flood beam will maintain the storage surface at two definite potentials above and below the critical potential, that is at the collector potential and the cathode potential. Moreover the storage surface maintained at two definite potentials will control the flood beam transmitted through the target producing on the fluorescent screen a visible image of high and low tones corresponding to the electric charge pattern written by the writing beam. The visible image does not disappear until erasing operation. For erasing, the collector potential is reduced to a suflicientlylow value while the whole storage surface is flooded by the flood beam, and then gradually restoring the collector potential to the original level. As the portions of the storage surface which have been written are maintained in condition of equilibrium, reducing the potential of the collector will result in the lowering. of the potential of the storage surface. Therefore if the collector poten-- tial is lowered sufliciently, the potential of the written portions will be lowered below the critical potential and then lowered down to near zero volt. During the lowering range of the potential of the storage surface, when the collector potential is gradually restored to the original value so that the electrostatic coupling with the collector may not cause the potential of the storage surface to jump above the critical potential, the storage surface will finally become to a condition of equilibrium near zero volt, thus effecting erasing operation.

Although various operations were described separately for the purpose of explanation, it will be clear that writing and reading out operation can be effected simultaneously by emitting the flood beam constantly.

As can be clearly understood from the foregoing descriptions regarding the construction and operation of the bistable writing type storage tube, even a target not provided with a back electrode can be utilized as the target of a bistable writing type storage tube. Considering now the functions of the back electrode normally used heretobefore in the conventional bistable writing type storage tube, the first function thereof is to support mechanically the entire assembly of the target. -In the target according to this invention this supporting function is provided by the metal mesh serving as the reference electrode of the storage surface. In order to set the potential of the storage target by means of said reference electrode, in the prior target, the potential was set by the actions of the collector and the back electrode on the other hand, in accordance with this invention, the collector in the form of a metal mesh functions to that end. As described hereinabove, with only one electrode the desired object can be attained. Another function of the back electrode is to fix the potential of the portion of the dielectric material other than the storage surface. By setting the potential of this portion to a value near zero volt, it is possible to provide an image having contrast. It has been recognized that the portions of the storage surface Which were not written are at the state of equilibrium near zero volt, but actually the state of equilibrium is reached at a point somewhat more positive than zero volt, and the other electrodes near the storage surface are maintained at substantial positive potentials so that it is not possible to perfectly intercept the transmission of the flood beam. As a result the back ground will have an appreciable brightness resulting in a poor contrast of the written pattern. In prior target, however, this disadvantage can be substantially reduced because the back electrode is maintained at a potential near zero whereas in the storage tube utilizing the target of this invention absence of the back electrode may substantially reduce the contrast. It is well known in the art that to impress a suitable positive pulse voltage upon the collector, or the back electrode or both of them in order to increase contrast of a bistable writing type storage tube utilizing a conventional target. Also in the bistable writing type storage tube utilizing the target of this invention a suitable positive pulse voltage applied to the collector thereof results in similar merits as in the prior storage with negligible reduction of the contrast.

The reason for the necessity of providing a back electrode for a target of a prior storage tube is believed to be clearly understood when one considers the history of the development of the bistable writing type storage tubes. More particularly it has been usual to use a target in the storage tube of the construction wherein wires of a metal mesh are covered by a dielectric material and the collector mesh is disposed on the side of the dielectric material at a point spaced therefrom by a suitable distance. In such a case the role of the back electrode has been very important. However it was found that, such an arrangement is not suitable from the standpoint of the operation of the bistable writing type storage tube and that it is desirable to arrange the collector in close proximity of or in contact with the surface of the dielectric material. When arranging the collector close to or in contact with the dielectric material, there was a fear that the applied dielectric material may peel off and this is the reason why it has been required to fabricate the collector from a thin mesh and soft metal wires such as aluminium. However with a construction wherein the collector mesh is in contact with the dielectric material the role of the back electrode is greatly reduced and we have affirmed theoretically and experimentally that the target may be constructed in the form of this invention.

A further feature of this invention is that thetarget for use in storage tubes will not be damaged by electric breakdown. Because voltages existing among various portions of the target during operation are the voltages existing between the collector and the portions of the storage surface that is maintained at the cathode potential of the flood gun and between the portions of the storage surface that is maintained near the collector potential and the portions that is maintained near said cathode potential. Even when an electric breakdown occurs only the electric charge stored in the electrostatic capacities between said portions are discharged so that there is no fear of damage as compared to the previous target wherein a voltage is normally impressed between the back electrode and the collector electrode. Further the fact that the collector is made of a nickel mesh which is more rigid than formerly used aluminium mesh contributes to reduce the possibility of damage.

Since the term the maximum writing speed means the maximum permissible writing speed necessary to bring the potential of the storage surface above the critical potential at the time of Writing, higher maximum writing speed can be obtained as the electrostatic capacity existing between the storage surface and other electrodes is decreased. In prior targets, there were electrostatic capacities between the storage surface and collector and also between the storage surface and the back electrode, Whereas in the target according to this invention, the electrostatic capacity exists only between the storage surface and the collector thus enabling to increase the maximum writing speed.

It should be understood that this invention is not limited to the particular embodiment illustrating a bistable wriing type storage tube utilizing a target wherein a dielectric material and a single metal mesh are combined into a substantially unitary structure and the metal mesh is used as the collector electrode.

Referring now to FIG. 3a illustrating another embodiment of the target of this invention there is shown a target 30 comprising a metal mesh 31 and a coating of dielectric material 32 on one side of the metal mesh facing the electron guns, as shown in FIG. 3a. Alternatively, when applying the dielectric material 32, a portion of the metal mesh may be masked so as to expose a portion 34 a of the base metal mesh facing the electron guns to cause the metal mesh to act effectively as the collector, as shown in FIG. 3b. In the embodiment shown in FIG. 3b, there is shown a construction of the target which can be obtained where the number of the Wires of the masking mesh (not shown) and that of the base mesh 31 are equal and these meshes were arranged to align each other. However it is to be understood that the number of wires of the masking mesh and that of the base mesh are not necessarily -be equal. Alternatively these meshes can be arranged so that their wires superpose at a suitable angle.

FIGS. 4:: and b show a still further modification of the target embodying this invention. As shown in FIG. 4a a material having a large secondary electron emission ratio, for example, magnesium fluoride 42 is vapor deposited on one surface of an insulator mesh 41 made of a dielectric insulator such as a photosensitive glass and the like and a metal mesh 43 is formed on the magnesium fluoride. This metal mesh 43 can be prepared by using a well known vapor deposition technique or a separately prepared metal mesh can be brought close to the magnesium fluoride. Further the target can be constructed in a manner as shown in FIG. 4b wherein mesh shaped grooves 45 provided on one side of a mesh 44 made of dielectric material are filled with metal 46. It is to be understood that the number of wires of the insulator mesh and the angle between these wires and the metal mesh are by no means limited to those illustrated in this embodiment.

In view of the above, it will be evident that many modifications and variations are possible in light of the above teachings. It therefore is to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. In a bistable writing type storage tube including an evacuated envelope, a fluorescent screen disposed in said envelope to display a pattern, at least two electron guns and a storage target disposed between said fluorescent screen and said electron guns, one of said electron guns emitting an electron beam adapted to Write a potential pattern on said target corresponding to an input signal and the other of said electron guns emitting a flood electron beam adapted to maintain said target at two stable and definite potentials and to excite said fluorescent screen to display thereon a pattern corresponding to said potential pattern on said target, said target having a multiapertured metal electrode in the form of a mesh grid means, and a mesh of dielectric material forming a unitary structure with the metal electrode, the improvement therein wherein said mesh of dielectric material includes a substance having large secondary electron emission ratio on one side of said dielectric mesh and said metal electrode is formed on said substance.

2. A tube according to claim 1 wherein said dielectric mesh has a relatively low secondary emission ratio.

3. A tube according to claim 1 wherein a mesh shaped groove is provided on one urface of said dielectric mesh and metal fills in said groove forming said metal electrode.

4. A tube according to claim 1 wherein said metal electrode has an exposed portion on the surface of said dielectric mesh facing said fluorescent screen.

5. A tube according to claim 3 wherein said metal electrode has an exposed portion on the surface of said dielectric mesh facing said fluorescent screen.

References Cited UNITED STATES PATENTS 2,401,786 6/1946 Law 313-68 2,788,467 4/1957 Smith 315l2 2,790,929 4/1957 Herman et al 31512 2,795,727 6/1957 Haeff 31512 2,824,249 2/1958 Hansen 313--68 2,896,106 7/1959 Burns et al 313-68 2,908,836 10/1959 Henderson 31368 OTHER REFERENCES RCA Technical Note No. 354, June 1960, by Hook and Stone on Means for Preventing Loss in Resolution in Display Storage Tubes.

JAMES W. LAWRENCE, Primary Examiner.

V. LAFRANCHI, Assistant Examiner. 

1. IN A BISTABLE WRITING TYPE STORAGE TUBE INCLUDING AN EVACUATED ENVELOPE, A FLUORESCENT SCREEN DISPOSED IN SAID ENVELOPE TO DISPLAY A PATTERN, AT LEAST TWO ELECTRON GUNS AND A STORAGE TARGET DISPOSED BETWEEN SAID FLUORESCENT SCREEN AND SAID ELECTRON GUNS, ONE OF SAID ELECTRON GUNS EMITTING AN ELECTRON BEAM ADAPTED TO WRITE A POTENTIAL PATTERN ON SAID TARGET CORRESPONDING TO AN INPUT SIGNAL AND THE OTHER OF SAID ELECTRON GUNS EMITTING A FLOOD ELECTRON BEAM ADAPTED TO MAINTAIN SAID TARGET AT TWO STABLE AND DEFINITE POTENTIALS AND TO EXCITE SAID FLUORESCENT SCREEN TO DISPLAY THEREON A PATTERN CORRESPONDING TO SAID PO- 